Dual cathode for fluorescent lamps



March 31, 1970 T. JyEMlDY 3,504,218

DUAL CATHODE FOR FLUORESCENT LAMPS Original Filed March 23. 1966 I 2 Sheets-Sheet 1 FIG. I FIG. 2

FIG. 3

" RAPID START BALLAST N v PRE- HEAT v BALLAST STARTER U. ATTORNEZ March 31; 1970 Original Filed March 23, 1966 FIG. 5

'r. J. EMIDY ETAL DUAL CATHODE FOR FLUORESCENT LAMPS 2 Sheets-Sheet 2 RAPID START BALLAST FIG. 6

- PRE-HEAT BALLAST STARTER INVENTORS THOMAS J EMIDY WALTER H. SIMSON LUKE THO'RINGTON ATTORNEYS United States Patent US. Cl. 313212 12 Claims ABSTRACT OF THE DISCLOSURE A cathode structure for a fluorescent lamp for use in rapid start and pre-heat type ballast circuits comprising a main and an auxiliary cathode at each end of the envelope in which the main cathode is connected to receive heating current and an arc discharge potential. The main cathodes operate to establish the arc discharge therebetween until substantially exhausted of electron emissive material at which time the arc discharge is transferred to between the auxiliary cathodes. The auxiliary cathodes are connected to receive only the are discharge potential and when they operate they place electron emissive material onto the main cathodes to permit them to operate again.

This application is a continuation of Ser. No. 536,888, filed Mar. 23, 1966, now abandoned.

Fluorescent lamps have been designed to operate with optimum results depending on the type of ballast circuit with which the lamps are to function. This was especially true during the earlier days of the art when preheat lamps were designed only for use with preheat ballast circuitry without compromise for use with any other ballast circuit. Later in the art, the rapid start lamp was designed for use only with rapid start ballast circuitry without compromise for use with any other circuit. More recently, and commonly the practice of most fluorescent lamp manufacturers, the rapid start lamp has been compromised to operate in both rapid start and preheat ballast circuits without any apparent change in the fundamental lamp design. It is common knowledge in the art, however, that sacrifices in efliciency result from the compromise depending on the circuit in which the rapid start lamp is used; the lamp operating with least efiiciency in preheat circuits.

It is the purpose of this invention to provide a cathode structure which will function with optimum results when operated in either rapid start or preheat ballast circuits.

This invention relates to low pressure discharge lamps such as fiourescent lamps comprising two pairs of thermionic electrodes sealed into opposite ends of an elongated tube having an interior phosphor coating and containing mercury vapor and an inert gas. More specifically the invention relates to low pressure discharge lamps designed to operate efiiciently in either rapid start or preheat circuit applications.

In the design of the cathode structure, detailed later in this disclosure, the basic functions of the dual purpose cathode structure are as follows:

(1) One half of the cathode structure (hereafter called the auxiliary cathode) is connected electrically, so as to function continuously during the life of the lamp as the lamp starting electrode. This function applies to both rapid start and preheat operation.

(2) The remaining half of the cathode structure (hereafter called the auxiliary cathode) is connected electrically, so as to function as the operating electrode at an interval in lamp life when the oxide coating contained in 3,504,218 Patented Mar. 31, 1970 the starting electrode has diminished to the oint when it ceases the function as an operating electrode.

For the purpose of illustration an embodiment of the invention is shown in the accompanying drawings in which:

FIG. 1 is an isometric side view of a cathode structure;

FIG. 2 is a top view of a cathode structure;

FIG. 3 diagrammatically illustrates the circuit arrangement for rapid start flourescent lamps employing the cathode structure of this invention;

FIG. 4 is a similar diagrammatic circuit illustration of a preheat circuit for fluorescent lamps employing the cathode structure of this invention;

FIG. 5 is a view similar to FIG. 3, showing a modified connection for the double cathodes; and

FIG. 6 is a view similar to FIG. 4 showing a modified circuit connection for the double cathodes. I

In FIG. 1 the cathode structure is shown mounted in a glass stem press 22 and flare assembly 8 which is provided to seal the end of an elongated fluorescent lamp envelope.

The assembly 8 includes the exhaust tube 6 and the aperture 10 providing the means for processing the fluorescent lamp envelope towards finished assembly. Lead in wires 12, 14 and 16 pass through assembly 8 and so spaced in the stem press 22 to provide equal distance between lead-in wires 12 and 16; 14 and 16. Stem press 22 is especially configurated, as shown in FIG. 1 and FIG. 2, to support the dual purpose cathode structure.

The included angle formed by main and auxiliary cathodes 20 and 18 is specified as -45 for optimum results. It is pointed out, however, that the included angle between the cathodes of a pair is not critical, the primary condition being that barium will be deposited on the starting (main) electrode atthe time when the adjacent (auxiliary) elecrode is functioning as the operating electrode. The purpose of this is to insure that the starting electrode will be supplied with a suflicient quantity of emission material to establish the inital arc. The plane of the cathode structure, wth reference to the axis of the fluorescent lamp envelope, may be perpendicular as shown, but need not be. Cathodes 18 and 20 used in the dual structure utilize a multi-turn overwound design wtih parameters commonly employed by the industry for preheat-rapid start fluorescent lamps.

In the processing of the fluorescent lamp envelope with a sealed-in member 8 at each end, lead-in wires 12 and 14 provide the means for activating the cathodes 18 and 20 coated with the usual alkaline earth metals common to the art. Either pair of lead-in wires 12 and 16 or 14 and 16 may be used to provide the electrical connections to the lamp base contact pins. The remaining leadin wire 12 or 14, whichever is not selected for the electrical connection, may be either short circuited to leadin wire 16 or cut from the assembly 8.

In the form of the invention shown in FIGURES 3 and 4, the lead-in wire 12 or 14, in the case illustrated the lead-in wire 14, is cut off short and left unconnected to the circuit.

On the other hand, the system of FIGURES 5 and 6 show the modified arrangement wherein the lead-in wire 12 or 14, in the case illustrated the lead-in wire 14, is connected to the lead-in wire 16. In other words, the cathode 18 is short circuited.

It is noted that the cathodes 18 and 20 of each pair,

electron emissive coatings well known in this art, such as the usual alkaline earth oxides, including, if desired, the usual quantity of zirconium oxides. The inert gas fillings for the envelope will be those usually employed including neon, krypton and the like, as well as mixtures thereof, all as is well understood in this art. The lamp envelope, diagrammatically illustrated in FIGURES 3 to 6 inclusive at 24, will have the usual phosphor coating 26, which is normally placed on the inner wall of the tube as indicated. In the circuits of FIGURES and 6, wherein the cathodes 18 are shorted upon themselves, the chief advantage of this variation is that during the latter stages of the lighting of the lamp there will be less wattage dissipation by reason of conductance through the cathode 18 itself than is the case shown in FIGURES 3 and 4 where the corresponding lead 14 of this cathode is disconnected.

During the operation of a fluorescent lamp utilizing the dual purpose cathode structure the starting of the lamp is initiated by applying filament heating current to the main cathodes which are electrically connected across the contact pins of the lamp bases. This cathode will operate as both the starting electrode and operating electrode until an interval in life when its emitting properties cease to function as an operating electrode but remain adequate as a starting electrode. At this interval the adjacent auxiliary cathode serves as the operating electrode.

It may be helpful to note that during the exhaust cycle the pairs of cathodes, cathodes of both embodiments of these lamps are treated out in series by passing currents through leads 12 and 14. In the initial operation of the completed lamp the main cathodes 20, with the lamp connected in either rapid start or preheat ballast circuits, are energized with the heating current in the usual way. The cathodes have the ballast potential thereacross so that they strike an arc and act as the operating cathode until they are completely stripped of emissive material. At this stage of the life of the lamp the lamps will still be started by heating the cathodes 20, but during operation the arc will shift to the auxiliary cathodes 18 with the ballast transformer potential still across the electrodes 20 which are connected to the electrodes 18 and the arc stream completing the electrical circuit between the auxiliary cathodes 18. In this mode of operation some emission material will be evaporated or sputtered otf and condensed on the cathodes 20 during operation. When the lamp is restarted it will again begin operation by the striking of the are between the cathodes 20 by reason of the thin film of emission material previously received. Almost immediately, however, after starting the are dis charge will transfer to the cathodes 18 and this operation will be repeated until all the emission material is stripped from the cathodes 18, signalling the end of the life of the lamp.

What is claimed is:

1. A fluorescent lamp operable from a source of voltage having two terminals comprising a sealed envelope (24), an auxiliary and a main cathode (18 and 20) each of which has an electron emissive coating thereon mounted at each end of said envelope to have an included angle of less than 180 therebetween, the two cathodes of each pair being in an opposing relationship so that one cathode of each pair can receive electron emissive material from the other cathode of the pair as a said cathode maintains the arc discharge thereon, a pair of leads (12, 16) connected across the two terminals of only said main cathode (20) at each end of the envelope, means for connecting each of said leads to a respective terminal of the voltage source for supplying heating current to each said main cathode and an arc discharge potential from the source across the terminals of said main cathodes of each of the two cathode pairs to initiate and maintain an arc discharge between said main cathode (20) of each pair until a said main cathode is substantially exhausted of emissive material, means connecting one terminal of the auxiliary cathode (18) of each cathode pair to only one of said leads (16) to receive only the arc discharge potential so that the arc will still be maintained by the auxiliary cathode (18) of a cathode pair when the said main cathode of a cathode pair is substantially exhausted of emissive material, said main cathode (20) of a cathode pair receiving emissive material from the auxiliary cathode (18) of the pair when the said auxiliary cathode maintains the are discharge to thereby enable the said main cathode of the cathode pair of subsequently initiate the arc discharge, and means (8, 14) for permanently holding the other terminal of each of said auxiliary cathodes at an insulated portion of said envelope permanently out of electrical contact with all other physical conductive components of the lamp.

2. The fluorescent lamp of claim 1 wherein the in cluded angle is approximately or less.

3. In the combination of claim 2, the cathodes of each pair being positioned to form an included angle in the range of 40 to 45.

4. In the combination of claim 2, each pair of cathodes being located in a plane perpendicular to the longitudinal axis of said envelope.

5. The fluorescent lamp of claim 1 further comprising a stem press of electrical insulating material for each end of the lamp having first, second and third support wires thereon, said main cathode of each cathode pair mounted between said first and second support wires of a respective stem press which two support wires also form the pair of leads of the first means, the auxiliary cathode of a pair being connected between said second support wire and one end of the third support wire, the other end of said third support wire terminating interior of its respective lamp end and being held in the stem press in an electrically insulating position.

6. In the combination of claim 4, the included angle between said cathodes being in the approximate range of 40 to 45.

7. A fluorescent lamp operable from a source of volt age having two terminals comprising a sealed envelope (24), an auxiliary and a main cathode (18, 20) each of which has an electron emissive coating thereon mounted at each end of said envelope to have an included angle of less than therebetween, the two cathodes of each pair being in an opposing relationship so that one cathode of each pair can receive electron emissive material from the other cathode of the pair as a said cathode maintains the arc discharge thereon, a pair of leads (12, 16) connected across the two terminals of only said main cathode (20) at each end of the envelope, means for connecting each of said leads to a respective terminal of the voltage source for supplying heating current to each said main cathode and an arc discharge potential from the source across the terminals of said main cathodes of each of the two cathode pairs to initiate and maintain an arc discharge between the said main cathode (20) of each pair until a said main cathode is substantially exhausted of emissive material, means connecting one terminal of the auxiliary cathode (18) of each cathode pair to onl one lead to receive only the arc discharge potential so that the arc will still be maintained by the auxiliary cathode (18) of a cathode pair when the said main cathode of a cathode pair is substantially exhausted of emissive material, said main cathode (20) of a cathode pair receiving emissive material from the auxiliary cathode (18) of the pair when the said auxiliary cathode maintains the arc discharge to thereby enable the said main cathode of the cathode pair to subsequently initiate the arc discharge, and means for permanently physically electrically connecting the other terminal (14) of each of said auxiliary cathodes to said one terminal of the said auxiliary cathode.

8. The fluorescent lamp of claim 7 wherein the included angle is approximately 90 or less.

9. In the combination of claim 8, the cathodes of each pair being positioned to form an included angle in the range of 40 to 45.

10. In the combination of claim 8, each pair of cathodes being located in a plane peripendicular to the longitudinal axis of said envelope.

11. The fluorescent lamp of claim 8 further comprising a stem press of electrical insulating material having first, second and third support wires thereon, said main cathode of each cathode pair mounted between the first and sec- 10 ond support wires of a respective stem press which two support wires also form the pair of leads of the first means, the auxiliary cathode of a pair mounted between the second and third support wires.

References Cited UNITED STATES PATENTS 2,141,933 12/1938 Perroit. 2,351,254 6/1944 Elmendorf. 2,411,679 11/1946 Cox et al. 2,659,835 11/1953 Germer. 3,328,622 6/1967 Toomey.

JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R.

12. In the combination of claim 11, the included angle 15 315-93 Patent No. 3,504,218 March 31, 1970 Thomas J. Emidy et a1.

r appears in the a'bcve identified atent are hereby corrected as It ie certified that erro t and that said Letters P shown below:

Column 4, line 12, rt to cancel the comma. cancel "of" and inse Signed and sealed this 29th day of September 1970 (SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

